Caffeine consumption: How much is too much?

Chocolate, coffee and cola are perhaps three of your favourite consumables; however, they are also three caffeine-rich substances which all contribute to your daily caffeine consumption. According to the BBC, people should not exceed 400mg caffeine a day, and this limit halves for pregnant women, for which only 200mg/day is recommended.

Coffee Beans

But how much does 400mg really correspond to? From the table below we can see that it is only 4 cups of instant coffee, or 10 cans of cola, or 16 bars of milk chocolate.


Amount of caffeine (Estimated)

One mug of filter coffee


One mug of instant coffee


One can of energy drink


One mug of tea


One 50g bar of dark chocolate


One can of cola


One 50g bar of milk chocolate


Table 1: Estimated amount of caffeine in products. Source: BBC

What actually is caffeine?

Caffeine is a chemical produced by several plants in order to kill or harm animals, particularly insects, which try to feed on them. The effect of the molecule in humans is to stimulate the central nervous system, heart rate and respiration. It is believed to function by reducing the ability of adenosine, which naturally slows down cell activity, to bind to receptors in the brain. This is because caffeine is a similar shape to adenosine and therefore it can bind to the adenosine receptors.

Another effect of caffeine consumption is that it causes epinephrine (adrenaline) to be released. This causes several changes in the body including causing the heart to beat faster; the blood pressure to rise; and the liver to release sugar into the bloodstream for extra energy.

Why is too much caffeine bad for us?

There are several consequences of consuming too much caffeine. These include:-

In the short-term:-

  • Shaking
  • Headaches
  • Increased urination
  • Nervousness
  • Increased blood pressure

In the long-term:-

  • Addiction
  • Trouble sleeping
  • Stained teeth

Potential risks in pregnant women:-

  • Higher risk of miscarriage
  • Low birth weight of baby


Stopping caffeine consumption

If you are considering stopping or reducing your caffeine intake then, like all addictive drugs, you may experience some withdrawal symptoms. These may include headaches, muscle aches, irritability and an inability to concentrate. The symptoms will normally begin between 12 and 24 hours after your last caffeine consumption and climb to their worst point around 24 and 48 hours. Thankfully, the symptoms will normally stop within a week.


Why you definitely shouldn’t give caffeine to dogs

Whilst a caffeine overdose can make us humans feel rather unwell, it can be lethal in some animals, such as small dogs and cats. So beware of leaving ground coffee or teabags lying around in places where small animals can get at them!

Further reading:

April Cashin-Garbutt

Written by

April Cashin-Garbutt

April graduated with a first-class honours degree in Natural Sciences from Pembroke College, University of Cambridge. During her time as Editor-in-Chief, News-Medical (2012-2017), she kickstarted the content production process and helped to grow the website readership to over 60 million visitors per year. Through interviewing global thought leaders in medicine and life sciences, including Nobel laureates, April developed a passion for neuroscience and now works at the Sainsbury Wellcome Centre for Neural Circuits and Behaviour, located within UCL.


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